1. Technical Field
This invention relates to a composite structure suitable for use in optical, optoelectronic or electronic applications. The structure includes a support wafer and a layered structure having at least one layer made of a material chosen from among monocrystalline materials. The composite structure is capable of dissipating heat caused by the operation of optical, electrical, or optoelectrical components.
2. Background Art
Dissipation of heat released by components in a useful layer becomes a critical problem when the operating frequencies of these components and/or their degree of miniaturization increases For example, in a CMOS application, the miniaturization of components and a reduced thickness useful layer exacerbates heat dissipation problems, particularly in cases wherein the useful layers are more or less thermally separated from a support substrate on which they were formed. In particular, CMOS components made as SOI (Silicon-On-Insulator), SiGeOI (SiGe-On-Insulator), GeOI (Ge-On-Insulator) or SGOI (Si/SiGe-On-Insulator) structures can be problematic as the temperature rises (which causes disturbances in the behavior of components). This is due to the fact that the oxide layer (which typically forms the insulating layer for these structures) forms a thermal barrier between a substrate and the useful layer. This type of SOI, SiGeOI, SGOI, GeOI structure may be fabricated by using a SMART-CUT® process, as described in U.S. Patent Publication No. 2004/0053477.
Components operating at a high power frequency (typically more than 900 MHz) can also cause temperature increases that could disturb or even damage them. To overcome this disadvantage, useful layers are typically made of a nitride semiconductor material with better charge carrying properties (high saturation rate of carriers at high voltage, high breakdown voltage, etc.) than materials such as AsGa. Such useful layers are used for High Electron Mobility Transistor (HEMT) type components. To form such nitride semiconductor-based layers, growth supports made of monocrystalline bulk SiC, bulk <111> Si, or bulk sapphire (Al2O3) are used, for which the lattice parameters are very similar to the lattice parameters of monocrystalline bulk <100> silicon. However, the thermal impedance properties of <111> Si and sapphire are still too high for some high power frequency applications that require greater dissipation of released heat, and although monocrystalline bulk SiC is generally used as a reference material concerning heat dissipation, this material is currently still too expensive to be practical.
U.S. Pat. No. 6,328,796 and U.S. Published application no. 2003/0064735 disclose composite structures made by bonding thin layers to support wafers. The support wafers are made of polycrystalline materials chosen for their thermal, electrical conductivity and thermal expansion properties (such as polycrystalline SiC substrates). A bonding layer made of a dielectric material is included that functions to improve the bond between the thin layer and the support wafer and to encourage the appearance of possible compliance phenomena. However, the materials and dimensions of the different layers and support wafers, and the methods of manufacturing the structure, are chosen to satisfy physical specifications such as thermal conduction, electrical conduction and thermal expansion. In order to satisfy these various specifications, a structure is chosen as a compromise solution, and it cannot give complete satisfaction. Therefore, the described composite structures are not optimized for high power frequency applications that require strong thermal dissipation properties.